1. Technical Field
The present application relates to an active stylus, a sensor controller for a stylus sensor, and a position input system and method based on such stylus and sensor controller; and more particularly to a position input system and method that utilize a bidirectional communications protocol between the stylus and the sensor controller.
2. Description of the Related Art
Various types of styluses are available that allow users to handwrite text and graphics on stylus-sensitive screens (sensors) of electronic devices, such as tablet computers, smart phones, etc. For example, an active electrostatic (capacitive) stylus includes a power source and a signal processor, and transmits signal by providing an electric charge corresponding to the transmission signal to an electrode provided at a tip of the stylus, to thereby cause a change in an electric field at or near a position indicated (pointed to) by the tip. A stylus-sensitive screen (sensor) of an electronic device includes a matrix of X- and Y-electrodes, and the above-described change in the electric field created by the stylus tip induces a corresponding change in an electric charge in the matrix electrodes at or near the stylus tip. A sensor controller coupled to the sensor and/or a host processor of the electronic device detects such change in the electric charge in the matrix electrodes to thereby detect the transmission signal from the stylus. The sensor controller and/or the host processor then determine the position indicated by the stylus on the sensor based on the location of the matrix electrodes that detected the transmission signal.
Different types of active styluses have different stylus capabilities or functions, such as pen (stylus) tip pressure detection capability, how many different levels the pen (tip) pressure can be detected, pen orientation detection capability including pen twist (rotation) detection capability and pen tilt detection capability, different numbers and kinds of barrel buttons (switches) provided on the styluses, etc. Typically, a data format used in communication from a stylus to a sensor controller is rigidly configured in a given stylus-sensor system and incapable of supporting different and expanding variations of stylus capabilities and functions.
While it is possible for each stylus to always transmit its entire capability information to the sensor controller each time the stylus is used with (i.e., enters the sensing zone of) the sensor controller, such transmission of the entire capability information would take up multiple time slots or frames available in a given communications protocol. In a typical situation where one or more styluses are constantly entering and exiting the sensing zone of the sensor controller, the sensor controller may not be able to quickly acquire the capability information of each entering stylus to start communication with the stylus in a manner appropriate for the stylus's particular capability. This may lead to slow response time of the sensor controller and hence delay in establishing communication between the sensor controller and the active stylus. For example, the sensor controller may not be able to promptly receive pen orientation data from a stylus, even when the stylus is fully capable of transmitting such orientation data, simply because the sensor controller cannot quickly ascertain the stylus's orientation detection capability.